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This paper presents a fast iterative algorithm for passivity enforcement of large nonpassive macromodels that share a common set of poles. It is ensured that the maximum passivity violation is monotonically decreasing in each iteration step, and convergence to a passive macromodel is guaranteed. [ABSTRACT FROM AUTHOR]

Circuit modeling of high-frequency devices described by tabulated multiport parameters has generated immense interest during recent years. In most cases, equivalent circuit models (ECMs) are available to the designers, which correlate well with the measured parameters at lower frequencies, however, deviate at higher frequencies. Traditional efforts to improve ECMs are device specific, laborious, and ad-hoc in nature. In order to address these difficulties, this paper presents an efficient and automated algorithm to identify appropriate frequency-dependent elements for adding to the ECM at arbitrary locations so as to correct for high-frequency errors. The new method enables the designers to retain their existing physical models while providing a means to capture the high-frequency effects accurately. [ABSTRACT FROM AUTHOR]

Three types of three-line baluns are studied in this paper. The equivalent circuits of these baluns are derived using the model of coupled transmission lines. The balun designs with Chebyshev response can then be exactly synthesized. A complete design procedure of the baluns with second-, third-, and fourth-order insertion' loss functions is presented. Balun designs with wide bandwidths of more than 2 to 1 are achievable by this method. Some guidelines for practical realization are also suggested. A third-order balun design with a fractional bandwidth of 80% is given to demonstrate the proposed procedure. [ABSTRACT FROM AUTHOR]

Adjustable and reactive in-phase/quadrature (I/Q) generators with constant resistance are proposed for the first time in this paper with the properties of low loss, dual-band implementation, and high quadrature accuracy. The quadrature phase property and input matching of the I/Q generator can be achieved at all frequencies simultaneously by the constant-resistance I/Q generator. However, the magnitude balance of the dual-band I/Q generator is achieved at two designed frequencies. A 2.4/5.2-GHz I/Q down-converter and a 2.4/5.7-GHz single-sideband up-converter are fabricated using 0.35-sm SiGe BiCMOS technology. The dual-band I/Q generator along with two single-to-differential amplifiers is integrated to provide differential quadrature local oscillator signals for dual-band mixers. The magnitude imbalance and phase error between the I and Q channels of the down-converter are <1% and < 10, respectively, while the maximum sideband rejection ratio of the up-converter is up to 50 dB. Additionally, the operation bandwidth (sideband rejection ratio >30 dB) is 200 MHz at 2.4 GHz and 720 MHz at 5.7 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a calibrated measurement technique that enables phase and magnitude measurements of wideband multisines. This study is based on the use of a large-signal network analyzer (LSNA) performing harmonic sub-sampling and a fine frequency grid (20 MHz) comb generator calibrated using a high-frequency 50-GHz equivalent-time sampling scope. This comb generator is used as a harmonic phase reference generator for the calibration of the LSNA. The research reported here is applied to L-band multisine measurements, but it can be extended to higher microwave frequencies. The motivation of this study is to measure the multipactor phenomena effect in output RF multiplexers of satellite payloads. [ABSTRACT FROM AUTHOR]

A fully scalable and SPICE compatible wideband model of on-chip interconnects valid up to 110 GHz is presented in this paper. The series branches of the proposed multisegment model consist of an RL ladder network to capture the skin and proximity effects, as well as the substrate skin effect. Their values are obtained from a technique based on a modified effective loop inductance approach and complex image method. A CG network is used in the shunt branches of the model, which accounts for capacitive coupling through the oxide and substrate loss due to the electrical field, as well as the impact of dummy metal fills. The values of these elements are determined by analytical and semiempirical formulas. The model is validated by a full-wave electromagnetic field solver, as well as measurements. The simulated S-parameters of the model agree well with the measured S-parameters of on-chip interconnects with different widths and lengths over a wide frequency range from dc up to 110 GHz. [ABSTRACT FROM AUTHOR]

This paper is aimed at the investigation of the technical realization problem for wideband reflectometers on multiprobe measuring lines. A geometrical interpretation of the measurement procedure that uses multiprobe measuring lines is considered. The parametric optimization problem of reflectometer is formulated and solved by use of a minimax optimum criterion. The results of solving this problem are presented. Tabulated parametric optimization data for reflectometers with probe number N = 4, 5, 6 and with boundary frequency ratio up to 40 are given. Experimental investigation was carried out over the frequency range from 6 to 18 GHz using the simplified calibration procedure of multiprobe reflectometer. Experimental data have confirmed the validity of optimization results. [ABSTRACT FROM AUTHOR]

This paper presents a hardware implementation of a digital predistorter (DPD) for linearizing RF power amplifiers (PAs) for wideband applications. The proposed predistortion linearizer is based on a nonlinear auto-regressive moving average (NARMA) structure, which can be derived from the NARMA PA behavioral model and then mapped into a set of scalable lookup tables (LUTs). The linearizer takes advantage of its recursive nature to relax the LUT count needed to compensate memory effects in PAs. Experimental support is provided by the implementation of the proposed NARMA DPD in a field-programmable gate-array device to linearize a 170-W peak power PA, validating the recursive DPD NARMA structure for W-CDMA signals and flexible transmission bandwidth scenarios. To the best of the authors' knowledge, it is the first time that a recursive structure is experimentally validated for DPD purposes. In addition to the results on PA efficiency and linearity, this paper addresses many practical implementation issues related to the use of FPGA in DPD applications, giving an original insight on actual prototyping scenarios. Finally, this study discusses the possibility of further enhancing the overall efficiency by degrading the PA operation mode, provided that DPD may be unavoidable due to the impact of memory effects. [ABSTRACT FROM AUTHOR]

We have already proposed a triple-tuned voltage-controlled oscillator (VCO) for achieving an ultra-wideband characteristic. The triple-tuned VCO consists of an active device and three tuned circuits. The fabricated VCO has achieved the oscillation bandwidth of 5.6-16.8 GHz and the phase noise of —114.9 dBc/Hz +1-2.9 dB at 1-MHz offset from the carrier. In this paper, for the first time, the conditions that the VCO achieves the ultra-wideband characteristic are clarified by formulation and simulation. It is also clarified that a transistor of the larger emitter size is suitable for the wideband VCO. In addition, the performances of the proposed VCO are compared with other reported wideband VCOs. As a result, it is shown that the proposed VCO has achieved the lowest figure of merit in the C-K u-band. [ABSTRACT FROM AUTHOR]

This paper presents two fully integrated CMOS transmit/receive (T/R) switches with improved body-floating operations. The first design exploits an improved transistor layout with asymmetric drain-source region, which reduces the drain-source feed-through for body-floated RF switches. In the second design, a switched body-floating technique is proposed, which reconfigures the body-floating condition of a switch transistor in the ON and OFF states. Both designs are fabricated in a standard 0.13-μm triple-well CMOS process. With regard to 2-dB insertion loss, the switch with asymmetric drain-source achieves 28-GHz bandwidth, which is among the highest reported frequencies for CMOS T/R switches. The bandwidth of the switched body-floating design is 16.6 GHz. There is approximately 5 dB better isolation obtained in the switched body-floating design. With the resistive double-well body-floating technique, 26.5- and 25.5-dBm input 1-dB compression point (P1dB) are obtained, respectively. Both designs consume only 150 μm × 100 μm die area. The demonstrated T/R switches are suitable for high-frequency and wideband transceivers. [ABSTRACT FROM AUTHOR]

This paper deals with a dual-mode ring resonator fed by quarter-wavelength side-coupled lines. The resonator synthesis was developed so as to fix the central frequency, bandwidth, and transmission zeros frequencies, as well as the insertion loss in the passband. Based on this resonator, several bandpass filters were designed, which include the cascaded rings and the combination of such ring resonator with coupled line sections. Simulations are proposed throughout the paper to illustrate the various possibilities offered by the concept. The filters' experimental results in microstrip technology are also presented to validate the idea. [ABSTRACT FROM AUTHOR]

This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power amplifiers (PAs) affected by strong differential memory effects. Differential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coefficients associated with the lower and upper intermodulations tones. Using large-signal vector measurement with a large-singal network analyzer, a class-AB LDMOS RF PA is demonstrated to exhibit a strong differential memory effect for modulation bandwidth above 0.3 MHz. New frequency-selective RF and baseband predistortion linearization algorithms are proposed to separately address the linearization requirements of the interband and inband intermodulation products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with MATLAB simulations using a Volterra/Wiener PA model with memory effects. The baseband linearization algorithm is next implemented in a field-programmable gate array and experimentally investigated for the linearization of the class-AB LDMOS PA for two carrier wideband code-division multiple-access signals. The ability of the algorithm to selectively linearize the two interband and four inband intermodulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated experimentally at twice the typical fractional bandwidth. [ABSTRACT FROM AUTHOR]

In this paper, analysis of a rat-race coupler having three equal arms of arbitrary electrical length is presented. All of these couplers have lower characteristic impedances than the conventional 1.5-λ coupler and some of them have smaller electrical lengths. Bandwidths in terms of isolation, matching, amplitude, and phase imbalances are also discussed. A reduced-size rat-race coupler of length 19λ/18 at the operating frequency of 0.9 GHz has been fabricated in the microstrip line. Experimental results agree well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

In this paper, a new power divider concept, which provides high flexibility of transmission line characteristic impedance and port impedance, is proposed. This power divider is implemented on a parallel-strip line, which is a balanced transmission line. By implementing the advantages and uniqueness of the parallel-strip line, the divider outperforms the conventional divider in terms of isolation bandwidths. A swap structure of the two lines of the parallel-strip line is employed in this design, which is critical for the isolation enhancements. A lumped-circuit model of the parallel-strip swap including all parasitic effects has been analyzed. An equal power divider with center frequency of 2 GHz was designed to demonstrate the idea. The experimental results show that the equal power divider has 96.5% - 19-dB impedance bandwidth with more than 25-dB isolation and less than 0.7-dB insertion loss. In order to generalize the concept with an arbitrary power ratio, we also realize unequal power dividers with the same isolation characteristics. The impedance bandwidth of the proposed power divider will increase with the dividing ratio, which is opposite to the conventional Wilkinson power divider. Unequal dividers with dividing ratios of 1 :2 and 1 : 12 are designed and measured. Additionally, a frequency independent 180° power divider has been realized with less than 2° phase errors. [ABSTRACT FROM AUTHOR]

Sub-harmonic modulator and demodulator are presented in this paper using 0.13-μm standard CMOS technology for millimeter-wave (MMW) wireless gigabit direct-conversion systems. To overcome the main problem of local oscillator (LO) leakage in direct-conversion systems, the sub-harmonically pumped scheme is selected in this mixer design. An embedded four-way quadrature divider is utilized in the sub-harmonic Gilbert-cell design to generate quadrature-phases LO signals at MMW frequency. For broadband applications, a broadband matching design formula is provided in this paper to extend the operational frequency range from 35 to 65 GHz. To improve the flatness of conversion loss at high frequency, high-impedance compensation lines are incorporated between the transconductance stage and LO switching quad of the Gilbert-cell mixer to compensate the parasitic capacitance. The sub-harmonic modulator and demodulator exhibit 6 ± 1.5 dB and 7.5 ± 1.5 dB measured conversion loss, respectively, from 35 to 65 GHz. For MMW wireless gigabit applications, the gigabit modulation signal test is successfully performed through the direct-conversion system in this paper. To our knowledge, this is the first demonstration of the MMW CMOS sub-harmonic modulator and demodulator that feature broadband and gigabit applications. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate an SiGe HBT ultra-wideband (UWB) low-noise amplifier (LNA), achieved by a newly proposed methodology, which takes advantage of the Miller effect for UWB input impedance matching and the inductive shunt-shunt feedback technique for bandwidth extension by pole-zero cancellation. The SiGe UWB LNA dissipates 25.8-mW power and achieves S11 below -10 dB for frequencies from 3 to 14 GHz (except for a small range from 10 to 11 GHz, which is below -9 dB), fiat S21 of 24.6 ± 1.5 dB for frequencies from 3 to 11.6 GHz, noise figure of 2.5 and 5.8 dB at 3 and 10 GHz, respectively, and good phase linearity property (group-delay variation is only ±28 Ps across the entire band). The measured 1-dB compression point (P1 dB) and input third-order intermodulation point are -25.5 and -17 dBm, respectively, at 5.4 GHz [ABSTRACT FROM AUTHOR]

This paper proposes a bandwidth-compensation method for miniaturized filters based on short-ended parallel coupled lines. Capacitive loading of such coupled lines is a relatively simple means of reducing the line lengths. In this study, a method is developed that predicts exactly the degree of reduction in the fractional bandwidth due to miniaturization. Using this method, the fractional bandwidth of the prototype coupled line filter can be adjusted, enabling miniaturized filters to maintain the targeted fractional bandwidth. The proposed bandwidth-compensation method applies for any type of filters with coupled lines realized with various transmission lines, with uniform or nonuniform line lengths. Experimental results are also presented that verify the validity of the method. [ABSTRACT FROM AUTHOR]

This paper demonstrates for the first time a tunable bandpass filter with simultaneous frequency and bandwidth control using a combination of ferroelectric barium-strontium-titanate capacitors and cantilever microelectromechanical systems (MEMS) switches. The center frequency of the filter is tuned in a continuous fashion from 30 to 35 GHz with insertion loss ranging from 10 to 2.7 dB. The fractional bandwidth of the filter can also be independently controlled by a tuning scheme that uses MEMS switches to vary the inter-resonator coupling. The two-pole filter prototypes resulted in fractional bandwidths of 9.6% (wideband configuration) and 4.8% (narrowband configuration) for a tuning ratio of approximately 2:1. The third-order filters resulted in bandwidths of 7.8 % (wideband configuration) and 3.1% (narrowband configuration) for a passband tunable ratio of approximately 2.5:1. [ABSTRACT FROM AUTHOR]

A new compact microstrip rat-race hybrid with an octave bandwidth employing a novel frequency-independent coplanar waveguide (CPW) phase inverter is reported in this paper. The 270° branch of a conventional rat-race is replaced by a -99° branch, which is realized by a 90° microstrip line and the CPW phase inverter. A new microstrip-to-CPW transition is introduced for which a lumped-element model is devised to facilitate parameter optimization. The designed transition has an insertion loss less than 0.33 dB across the designed frequency band from 1.5 to 3.5 GHz. The footprint of the proposed design is reduced by 75% and shows almost 60% and 80% enhancements in the 0.5-dB mismatch bandwidth of amplitude and 10° mismatch bandwidth of phase, respectively, when compared with the conventional implementation. The proposed hybrid can be fabricated using a conventional printed-circuit and plated thru-hole technologies. [ABSTRACT FROM AUTHOR]

A wideband logarithmic amplifier is demonstrated in this paper using InP-InGaAs double heterojunction bipolar transistor technology. The amplifier uses cascaded gain stages including the limiting and unity amplifiers to achieve a piecewise approximation to the ideal logarithmic response. The performance of 43-dB dynamic range, 22-GHz bandwidth, and < ±2-dB log error is achieved. The integrated circuit consumes 650 mW and has a chip dimension of 1 × 0.8 mm². [ABSTRACT FROM AUTHOR]

One of the main trends in the evolution of radio receivers and other wireless device is to implement more and more of the receiver functionalities using digital signal processing (DSP). However, due to practical limitations in the analog-to-digital conversion process, some analog signal processing stages are likely to remain also in the continuation. With the ever-increasing demands for the system performance and supported data rates on one side, and the terminal flexibility and implementation costs on the other, the requirements for these remaining analog front-end stages become extremely challenging to meet. Then, one interesting idea in this context is to apply sophisticated DSP-based techniques to compensate for some of the most fundamental nonidealities of the receiver analog front-ends. In this paper, we focus on developing and demonstrating novel digital techniques to mitigate the effects of harmonic and intermodulation distortion in wideband multicarrier or multichannel receivers using adaptive interference cancellation. The approach in general is practically oriented and largely based on analyzing and processing measured real-world receiver front-end signals. The obtained results indicate that the proposed compensation technique can be used to suppress nonlinear distortion due to receiver front-end sections under realistic signaling assumptions [ABSTRACT FROM PUBLISHER]

This paper reports an experimental and computational study of substrate integrated waveguides (SIWs) optimized for use as ultrahigh-speed bandpass waveguiding digital inter- connects. The novelty of this study resides in our successful design, fabrication, and testing of low-loss SIWs that achieve 100% relative bandwidths via optimal excitation of the dominant TE10 mode and avoidance of the excitation of the TE20 mode. Furthermore, our optimal structures maintain their 100% relative bandwidth while transmitting around 45° and 90° bends, and achieve measured crosstalk of better than -30 dB over the entire passband. We consider SIWs operating at center frequencies of 50 GHz, accommodating in principle data rates of greater than 50 Gb/s. These SIWs are 35% narrower in the transverse direction and provide a 20% larger relative bandwidth than our previously reported electromagnetic bandgap waveguiding digital interconnects. Since existing circuit-board technology permits dimensional reductions of the SIWs by yet another factor of 4:1 relative to the ones discussed here, bandpass operation at center frequencies approaching 200 GHz with data rates of 200 Gb/s are feasible. These data rates meet or exceed those expected eventually for proposed silicon photonic technologies. [ABSTRACT FROM AUTHOR]

In this paper, performances of stored-reference, transmitted-reference (TR), and energy-detection (ED)-based time-of-arrival estimation techniques are analyzed for impulse-radio ultra-wideband (IR-UWB) systems at sub-Nyquist sampling rates. First, an additive white Gaussian noise channel is considered to emphasize certain fundamental issues related to these different transceivers. In particular, energy collection characteristics and decision statistics are presented. Probability of accurate peak detection is analyzed for each transceiver, and receiver operating characteristics for the leading edge are derived. Effects of number of pulses per symbol and number of averaging symbols are investigated in detail. Then, realistic multipath channels are addressed, and various maximum-likelihood estimation approaches are investigated. A new estimator that jointly exploits the noise statistics and power delay profile of the channel is proposed, and a Bayesian estimator that (ideally) gives a lower bound is analyzed. Simulation results show that while ED and TR have better energy collection capabilities at low-rate sampling, they suffer from distributing the energy over time. [ABSTRACT FROM PUBLISHER]

This paper presents a mixed-signal frequency-domain implementation of the autocorrelation receiver used in the detection of ultra-wideband communication signals that are modulated with transmitted-reference signaling. The digital receiver architecture is based on samples provided by an analog-to-digital converter (ADC) in the frequency domain. Among the advantages of the new receiver are the relaxation of the conversion speed achieved by the inherent parallel architecture of the frequency-domain ADC and the flexibility and simplicity of an all-digital receiver architecture that follows the mixed-signal ADC radio front-end. The paper provides the symbol detection formulas and the corresponding system implementation and makes comparisons with the conventional time-domain implementations. Additionally, a time synchronization technique for the new receiver structure is proposed, which makes the receiver insensitive to any time offset at the pulse level. Furthermore, as a particular case of great practical interest, we consider a single bit for the ADC implementation, and we show with experimental results that the resultant frequency-domain mono-bit digital receiver provides a performance gain that increases with the number of frequency samples, when compared with its time-domain counterpart. [ABSTRACT FROM PUBLISHER]

This paper presents the ultra-wideband on-body radio channel modeling using a subband finite-difference time-domain (FDTD) method and a model combining the uniform geometrical theory of diffraction (UTD) and ray tracing (RT). In the subband FDTD model, the frequency band (3-9 GHz) is uniformly divided into 12 subbands in order to take into account the material frequency dispersion. Each subband is simulated separately and then a combination technique is used to recover all simulations at the receiver. In the UTD/RT model, the RT technique is used to find the surface diffracted ray path, while the UTD is applied for calculating the received signal. Respective modeling results from two- and three-dimensional subband FDTD and UTD/RT models indicate that antenna patterns have significant impacts on the on-body radio channel. The effect of different antenna types on on-body radio channels is also investigated through the UTD/RT approach. [ABSTRACT FROM PUBLISHER]

This paper presents an ultrawide-band (UWB) channel sounding scheme with a parametric channel estimation to seek accurate probing of the propagation channel. The channel sounder consists of a vector network analzer and synthetic array to measure spatial transfer functions. The measured data are then applied to a maximum-likelihood (ML)-based estimator. The concepts implemented in the ML-based parametric channel estimation are: 1) to probe frequency-dependent effects in magnitude and phase of propagation paths and 2) to incorporate with robust concept of direction finding, namely, the spherical wavefront model of incident waves. The whole frequency band was divided into subbands, and the estimation of magnitude and phase was conducted in each subband. The spherical wavefront model includes a new model parameter, curvature radii, which is not covered in the conventional plane wavefront model. Performances of the proposed parametric UWB channel estimation scheme was assessed by anechoic chamber tests. The test demonstrated that: 1) the frequency-dependent magnitude and phase were accurately detected if the path was resolved and 2) the spherical wavefront outperformed the plane wavefront to model measured data given the short-range environment. Furthermore, fundamental performance of the sounding scheme, i.e., angular and time resolutions, were also evaluated in the test. [ABSTRACT FROM PUBLISHER]

A six-channel multiplexer composed of parallel-coupled microstrip bandpass filters is developed. The passbands of the filters, i.e., channel frequencies, are 10, 12, 19, 21, 32, and 35 GHz. The operating frequency range of the multiplexer is so wide that a new method of harmonic suppression is devised for the filters designed at 10 and 12 GHz. The method is simple and does not require any change to the conventional parallel-coupled microstrip bandpass filter. A design procedure for the microstrip multiplexer is then introduced with a rule to set up initial conditions for better optimization. The designed multiplexer does not need any tuning elements, and the measurement results show insertion losses between 2.0–3.2 dB for all six channels. The multiplexer developed in this paper has been used in the wide-band transceiver system. [ABSTRACT FROM AUTHOR]

This paper proposes a new predistortion method using the gain expansion phenomenon in a Doherty amplifier. In the proposed structure, the drive stage Doherty amplifier, which has a gain expansion characteristic, precedes the final stage Doherty amplifier. The gain expansion characteristic compensates for the gain compression of the final stage amplifier and the overall linearity is improved based on an increase in the total output P1 dB compression point. Using a behavioral model, we simulated the effect of increasing the P1 dB point to the adjacent channel power ratio (ACPR) of the CDMA2000 signal. The experimental results show that the overall output P1 dB compression point is improved by 1.5 dB and the ACPR for the one-carrier CDMA2000 signal is improved by 8.5 dB. In addition, we tested a power amplifier with a four-carrier WCDMA signal to verify the validity of this configuration for wide-band applications. [ABSTRACT FROM AUTHOR]

In this paper, an augmented lookup-table-based Hammerstein predistorter is proposed for the first time in order to further improve the pre-correction capability of the traditional Hammerstein predistorter in the context of broad-band high-power wireless transmitters. The predistorter scheme consists of two separate modules, and its parameters are determined in two steps, which are: 1) static predistorter identification and then 2) dynamic part identification. The performance assessment of the newly proposed predistorter is carried out on a wireless transmitter prototype, which includes an L-band push-pull GaAs field-effect transistor 45-dBm peak-envelope power amplifier. Moreover, one- and three-carrier Third-Generation Partnership Projects frequency-division duplex wide-band code-division multiple-access signals are used as test signals to verify the robustness of this novel predistorter under different bandwidth signals. The linearized transmitter prototype output spectrum demonstrates noticeable superiority of the proposed augmented predistorter in suppressing the spectrum regrowth caused by the memory effects in comparison to the traditional Hammerstein predistorter. [ABSTRACT FROM AUTHOR]

This paper proposes a novel frequency channel blocking (FCB) scheme in mesh-topology millimeter-wave broad- hand entrance networks. In the FCB scheme, any frequency channel is determined to be blocked according to not only the network throughput, but also the newly defined fairness index. As the results, the FCB scheme yields better throughput and fairness performances with a little increase in computational complexity compared to the conventional scheme. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive wide-band digitally controlled RF envelope predistortion linearization system for power amplifiers (PAs). A field-programmable gate-array-based lookup table is indexed by a digitized envelope power signal, and instantaneously adjusts the input signal amplitude and phase via an RF vector modulator to compensate for the AM--AM and AM--PM distortion. The advantages of this predistortion architecture over conventional baseband digital approaches are that a 20%-33% wider correction bandwidth is achievable at the same clock speeds, and linearization can be performed without the need for a digital baseband input signal. The timing match between the input RF signal and predistorting signal, which is one of the critical factors for performance, was investigated and adjusted to obtain optimum performance. Using three-carrier cdmaOne and wide-band multitone signals, the linearization performances for a 0.5-W GaAs heterostructure field-effect transistor, a 90-W peak-envelope-power (PEP) silicon LDMOS PA, and a 680-W PEP LDMOS PA were examined. In addition, the predistortion performance variation for different signals was studied in terms of signal envelope statistics, output powers, and PA power capacities. [ABSTRACT FROM AUTHOR]

A new combline filter structure with a continuous tunability for both the center frequency and bandwidth is presented in this paper. The passband-width tunability is achieved by placing variable coupling reducers between the filter resonators. The coupling reducers, operating as bandwidth control subnetworks, are designed as detuned resonators made up of a line segment ending in a variable capacitor. The proposed filter structure is experimentally validated with the design, construction in suspended stripline technology, and characterization of a low-cost filter prototype for terrestrial digital video broadcasting receivers operating in the UHF band (470-862 MHz). Other relevant factors, such as the intermodulation distortion produced by the varactors used to control the bandwidth electronically or the power-handling performance of the constructed filter, are also discussed. The reconfigurable filter module described in this paper is very suitable for the design of flexible multifunction receiver subsystems simultaneously supporting signals with a different bandwidth. [ABSTRACT FROM AUTHOR]

This paper reports on a novel lumped balun topology, the second-order lattice balun, with broad-band performance. The design is based on synthetic transmission lines operating as impedance transformers, The characteristic impedance of the synthetic transmission lines may be chosen to obtain inherent impedance transformation. An analytical investigation results in closed formulas for optimum performance over a given band-width. It is shown that it is possible to design for equal ripple in amplitude balance and input reflection coefficient. The phase balance is theoretically perfect over the entire bandwidth. The concept is experimentally validated by a 1-GHz prototype fabricated with surface mounted chip components. It exhibits an amplitude balance better than 0.5 dB and a phase balance better than ±8° over an octave bandwidth. The effective area of the prototype is 7 × 9 mm⊃. [ABSTRACT FROM AUTHOR]

In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constunt within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bundpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results ale compared with theoretical ones based on these equations. [ABSTRACT FROM AUTHOR]

For personal communication systems, the highest possible integration into monolithic technology of all RF functions are desirable. A frequency band around 60 GHz is assigned for future mobile communication fourth-generation systems (i.e., mobile broad-band systems concept). In this paper, the design and test of two monolithic class-A power amplifiers with 0.15 μm pseudomorphic heterojunction FET (PMHFET) technology is presented. One of the amplifiers is a three-stage cascade 50 Ω amplifier and the second is a balanced amplifier based on the previous one, but matched for integration on a waveguide carrier. A study on the accuracy of the passive elements and discontinuities models at 60 GHz was performed. Models for the microstrip discontinuities were obtained from electromagnetic simulation. In order to choose the best FET bias, a nonlinear model for the PMHFETs devices, based on continuous DC and AC measurements, were derived. For comparison purposes, the FET simulation results with a nonlinear model based on pulsed measurements are also presented. To avoid stability problems, at the device level an RC feedback network was introduced. A 1-dB compression point of 18 dBm was measured on-wafer for both amplifiers at 62 GHz with VDSbias=3.5 V. The three-stage and balanced amplifiers chip sizes are 3 mm×1.5 mm and 3 mm×4 mm, respectively [ABSTRACT FROM PUBLISHER]

In this paper, an extended Chebyshev function is proposed to adapt the matching condition of the power amplifier (PA) by introducing a new factor. A set of impedance functions can be directly calculated along with the variation of a new variable, and the first element extracted from the functions is distributed in a wide range. In addition, the impedance function whose first element is the closest to the output capacitance of the transistor can be easily read out and selected as the original matching network. The fundamental impedance of the selected function will be reached a good matching state, and the impedances out of band will be on the edge of Smith chart. To achieve better performances, the real frequency technique is applied to adjust the harmonic impedances preventing it from falling into the low-efficiency region. Two PAs with a relative bandwidth of 34% and 75% are implemented to validate the proposed approach. [ABSTRACT FROM PUBLISHER]

In a conventional differential phase shifter (DPS), to realize arbitrary phase shifts, the reference and main microstrip lines are of different lengths. This difference results in suboptimal integration density, which renders the wireless communication system implementation complex and bulky. This paper presents an equal-length multiway DPS based on metamaterials. The reference lines have identical dimensions and are of equal lengths with the main lines. The proposed structure covers a wide bandwidth by aligning the main line phase slope without degradation in return and insertion losses. A design optimization methodology is presented for wideband DPSs in the 0°–90° range. For demonstration, a six-way DPS has been designed and fabricated. The measurements show that the phase shifters have less than 5° differential phase stability and better than a 10-dB return loss, with an insertion loss less than 1.24 dB from 1.6 to 3.2 GHz. [ABSTRACT FROM PUBLISHER]

The new services available through smart devices require very high cellular network capacity. The capacity requirement is expected to increase exponentially with the forthcoming 5G networks. The only available spectrum for truly wideband communication (>1 GHz) is at millimeter wavelengths. The high free space loss can be overcome by using the directive and beam-steerable antennas. This paper describes a design and the measurement results for a lens antenna system for $E$ -band having 2-D beam-steering capability. Continuous beam-switching range of about \pm 4 {^{\circ }} \times \pm 17^{\circ } is demonstrated with the lens having the maximum measured directivity of 36.7 dB. Link budget calculation for backhaul application using the presented lens antenna system is presented and compared with the measurement results of the implemented demo system. [ABSTRACT FROM PUBLISHER]

This paper presents a modified Doherty configuration with extended bandwidth. The narrow band feature of the conventional Doherty amplifier is discussed in the view of the broadband matching. To extend the bandwidth, the post-matching architecture is employed in the proposed design. Meanwhile, broadband low-order impedance inverters are adopted to replace the quarter-wavelength transmission lines. Low-pass filter topologies are used to realize both the post matching network and the impedance inverters. A modified Doherty Power amplifier was designed and fabricated based on commercial GaN HEMT devices to validate the broadband characteristics of this configuration. The 6-dB backoff efficiencies of 47%–57% are obtained from 1.7 to 2.6 GHz (41.9% fractional bandwidth) and the measured maximum output power ranges from 44.9 to 46.3 dBm in the designed band. In particular, more than 40% efficiencies are measured at 10-dB backoff throughout the operation band. [ABSTRACT FROM PUBLISHER]

Broadband microwave complex permittivity measurements of nanodiamond powders are presented. Previous studies show that measurements of dielectric loss strongly correlate with the presence of nondiamond surface impurities. In this study, the frequency dependence of these losses is investigated using the microwave cavity perturbation (MCP) and broadband coaxial probe (BCP) methods. This allowed further understanding as to what mechanisms contribute to the microwave absorption (free electron conduction or dielectric loss from the disordered surfaces). A multimode MCP system is used which utilizes TM0np modes to provide partial spectral characterization. The MCP results revealed minimal frequency dependence, unlike any static conduction-related mechanism. The BCP measurements corroborate the MCP results with much higher spectral resolution, and further demonstrate that disorder related loss may dominate over free electron conduction from 1–10 GHz. From 0.1–1 GHz, free electron conduction has a greater influence with a characteristic 1/f dependence implying that conduction may dominate at lower frequencies. However, the BCP method, while repeatable, lacks in precision compared to the cavity method. Nonetheless, the major conclusion in this paper is that through simple microwave permittivity measurements, nondiamond carbon impurities in nanodiamond powders are measurable most likely because of disorder related losses as opposed to free electron conduction. [ABSTRACT FROM PUBLISHER]

A broadband SiGe power amplifier (PA) with double gain peaks for 5G applications is presented. The differential structure is widely adopted in millimeter-wave circuit design to decrease the impact of the source parasitic inductance that is induced by the bonding wires. Since differential PA results in a higher impedance transformation ratio of the matching network, differential PAs generally have narrower bandwidth than single-ended PAs. Through the bandwidth analysis of the matching network, the transformer used for interstage matching is elaborately designed to ease gain fluctuations. By controlling the stationary points of impedance transformation, the maximum available gain characteristic of a transistor, which decreases with increasing frequency, can be compensated. The gain curve of PA, thus, has double gain peaks within operational frequencies to make its frequency responses as flat as possible. The proposed PA for the frequency band from 27 to 37 GHz is fabricated in a standard 130-nm SiGe BiCMOS process, which occupies 0.36 mm2. Under the 2.5-V voltage supply, the SiGe PA exhibited a power gain of 33.5 dB and output power of 21.3 dBm with 24% power-added efficiency at 31 GHz. It achieves a 34% 3-dB small-signal S21 bandwidth from 27.3 to 38.5 GHz. [ABSTRACT FROM AUTHOR]

A new methodology for the design of single/multi-band power amplifiers (PAs) with dynamic load modulation (DLM) is presented. First, the topology for the output matching network (OMN) including the control varactor is selected. A comprehensive optimization of the OMN parameters is then developed by which varactor and transistor losses are considered to ensure maximum efficiency enhancement at each frequency. To verify the method, a dual-band PA with DLM is realized. Drain efficiencies of 75% and 60% at 685 MHz and 1.84 GHz, respectively, are measured at peak output power. At 10-dB output power back-off efficiencies of 43.5% and 49.5%, respectively, are obtained. Linearized modulated measurements with a 6.5-dB peak-to-average power ratio WCDMA signal show average drain efficiencies of 56% and 54% at 685 MHz and 1.84 GHz, respectively, at an adjacent channel leakage ratio of -\49 and - \47.5 dBc, respectively. The proposed method shows the effectiveness of applying an optimization process for the design of single- or multi-band DLM PAs. The results demonstrate that near-optimum performance may be obtained in terms of efficiency enhancement for a given transistor and varactor-based OMN, thus making DLM competitive against other load modulation techniques. [ABSTRACT FROM AUTHOR]

A novel application of an 8 \times 8 Butler matrix in broadband multiport measuring systems has been presented. The proposed measuring system consists solely of a single broadband 8 \times 8 Butler matrix and only one isolator allowing for measurements of all S-matrix coefficients of any two-port device. It has been shown that the properties of the applied 8 \times 8 Butler matrix allow to obtain high measurement accuracy, which has been estimated with a numerical procedure for a different number of applied power detectors. The improved analytical procedure of calibration necessary for the transmission coefficient measurement has been presented. Performance of the proposed measuring system has been experimentally verified in a wide frequency range of 2–3.5 GHz, by measurements of S-parameters of seven exemplary attenuators and a narrowband bandpass filter. The measurement results are very close to the values obtained with the use of a commercial vector network analyzer. [ABSTRACT FROM AUTHOR]

Software-defined radio technology is experiencing more and more attention in modern communication and radar systems. The main practical challenge in deploying such technology is related to achieving sufficient linearity and spurious-free dynamic range in the RF front-end, especially in low-cost mass-product devices. This paper focuses on the analysis and digital mitigation of nonlinear distortion in software-define radio devices, building on wideband multicarrier/multiradio direct-conversion receiver principle where a wide collection of radio frequencies is in-phase/quadrature down-converted as a whole. A complete behavioral model for the total nonlinear distortion of the whole receiver chain is first derived, taking into account the third-order nonlinear distortion effects in all individual components, namely, RF low-noise amplifier, in-phase/quadrature mixer, and baseband in-phase/quadrature amplifiers. Stemming from this modeling, an adaptive digital feed-forward linearization structure is then developed to efficiently mitigate the joint nonlinear distortion of the whole receiver. The effectiveness of this approach is verified through extensive simulations and actual RF system measurements with a commercially available software-defined radio platform, which clearly outperforms the existing state-of-the-art methods that do not jointly consider RF and baseband nonlinearities. [ABSTRACT FROM PUBLISHER]

In spite of the FCC regulations, the coexistence of ultra-wideband (UWB) and narrowband (NB) systems is still an unsolved challenge. A UWB transmitter (TX) can severely degrade the performance of an IEEE 802.11a system. In this paper, a fully integrated analog impulse-radio UWB TX is presented that generates a novel UWB pulse with a tunable notch at the frequency of IEEE 802.11a system. The pulse has a 5.5-GHz bandwidth (BW), which makes it suitable for high-resolution high data-rate applications. The TX has a maximum pulse rate of 400 Mpulse/s and energy of 65 pJ/pulse with a power supply of 1.2 V. The measurement results show that the pulse has a 30-dB notch, and the TX power inside the BW of the NB system is less than -\78 dBm/MHz. The TX has a biphase modulation and has been fabricated in a 90-nm CMOS process. The proposed pulse meets the Federal Communications Commission mask for UWB systems. [ABSTRACT FROM AUTHOR]

Passive-mixer-first receivers have recently demonstrated flexible, low-noise, and high-linearity performance. Likewise, capacitive coupling element antennas have been demonstrated to be a viable choice for mobile handset integration. This paper combines these two advances into a single-antenna wideband receiver that achieves a 0.7–2.7-GHz reception band. The compact-size wideband tunable antenna achieves an efficiency of 45%–69% and occupies a volume of 2500 \ mm^3. The front-end integrated circuit achieves an input compression point of +5 dBm with a noise figure of 4 dB while occupying only 0.3 \ mm^2 of active die area. Additionally, an interface impedance study is performed to find the optimal impedances around the passive mixer and to demonstrate the different design tradeoffs of a passive-mixer-first receiver. A local oscillator duty-cycle adjustment circuit and its effect on the receiver performance is also presented. [ABSTRACT FROM PUBLISHER]

This paper presents, for the first time, the theoretical and experimental study of broadband rat-race coupler design with a tunable power dividing ratio. Wide fractional bandwidth (around 40%) is accomplished by the adoption of frequency compensating networks with specific derivatives of even- and odd-mode admittances. General formulation is analytically carried out to lay down the design principles of these networks. The proposed design also features wide tuning range (almost 20 dB), low insertion loss, high port isolation (over 25 dB), good return loss, simple structure, compact size, zero dc power consumption, and single voltage operation with a minimal number of tuning diodes. For demonstration, both simulated and measured results of a 1-GHz tunable rat-race coupler implemented on microstrip are shown. [ABSTRACT FROM PUBLISHER]

This paper presents a high-efficiency GaN Doherty power amplifier (PA) with 100-MHz instantaneous bandwidth for 3.5-GHz long-term-evolution (LTE)-advanced application. A modified load modulation network, employing an enlarged peaking amplifier to carrier amplifier power ratio and moderately increased load impedance of the carrier amplifier, is proposed for enhancing efficiency and achieving improved load modulation. To increase the power ratio and alleviate the influence of slight impedance mismatch, a proposed load impedance strategy and corresponding stepped-impedance matching network are adopted for high-efficiency and wideband operation. By tuning the carrier offset line, the inconsistency of efficiency, gain, and output power in the operation band can be alleviated. Measurement results show that the Doherty PA has a drain efficiency of approximately 40% with gain fluctuation less than 0.5 dB at 9-dB back-off power, and maximum efficiency of about 60% at saturation in the signal band of 3.4–3.5 GHz. By using the digital pre-distortion (DPD) technique, the Doherty PA achieves adjacent channel leakage ratio of about -48 dBc at an average output power of 40.4 dBm with efficiency of 42.5%, when driven by 100-MHz LTE-advanced signal. To the best of the authors' knowledge, this is the first high-performance result of linearization using conventional DPD technique with 100-MHz bandwidth signals for the GaN Doherty PA at 3.5-GHz frequency band thus far. [ABSTRACT FROM PUBLISHER]

This paper presents a tunable broadband monolithic microwave integrated circuit (MMIC) active directional coupler that demonstrates tuned coupling gains (from 3 dB to -6 dB) and tuned center frequencies. The active directional coupler consists of two broadband near 90^\circ phase shifters, two amplifiers between these phase shifters, and varactors at the connection nodes of the phase shifters and the amplifiers. It was designed and fabricated in a 130-nm process. For a 3-dB coupling gain, the 10-dB directivity bandwidth is 2.3 GHz (from 5.5 to 7.8 GHz). The amplitude imbalance is 3 dB \pm0.5 dB, the phase imbalance is 180^\circ \pm 5^\circ, and the noise figure is less than 8 dB in the range of 4 to 9 GHz. The return losses are better than 19 dB and the insertion loss is less than 1.2 dB in the range of 4 to 9 GHz. The measured IP1 dBs for 3-dB and 0-dB coupling gains at 6.7 GHz are 0.3 dBm and 1.8 dBm, respectively. The supply voltage is 1.2 V. The measured power consumptions at 3-dB, 0-dB, - 3-dB, and - 6-dB coupling gains are 22 mW, 6 mW, 3 mW, and 1 mW, respectively. The core chip area, including two on-chip DC bias inductors, is 470 \mum \, \times\,250 \mum. [ABSTRACT FROM AUTHOR]

This paper proposes a parametric method of frequency-dependent I/Q imbalance compensation for wideband quadrature modulators using the spectrum measurement of a radio frequency (RF) signal that is easily performed by a general-purpose spectrum analyzer. The proposed method empirically estimates the frequency-dependent circuit parameters using only the magnitude of the frequency spectrum of the RF signal that is fed back from the spectrum analyzer. The frequency dependency of the I/Q imbalance effect generated by the difference between the overall frequency responses of the I and Q branches is modeled by frequency-dependent circuit parameters. By dividing the entire signal band into several sub-bands, the transmit signals are predistorted per sub-band in the frequency domain. To estimate the frequency-dependent circuit parameters, in this study, the modified method of steepest descent developed for single-band compensation is extended to the frequency-domain sub-band compensation scheme. We demonstrate the compensation effect by implementing an automatic sub-band circuit parameter estimation system. [ABSTRACT FROM AUTHOR]